Mobile station and method for controlling mobile station side communication, base station and method for controlling base station side communication, and communication system

ABSTRACT

When emergency communication etc. is sent, it aims at preferentially dealing with the emergency communication etc. by a simple and effective method. It is a communication system in which a base station  100  and a mobile station  200   a  establish communication for emergency situation, in time of emergency, wherein the mobile station  200   a  switches an output adjustment from the normal mode to the emergency mode and sends the communication for emergency situation at the largest output possible. The base station  100  receives a strong radio wave from the mobile station  200   a  which sent the communication for emergency situation. The base station  100  continues to output suppression signals for suppressing signal intensity to the other mobile stations. The other mobile stations are suppressed by the near-far effect, and it becomes impossible for the base station  100  to receive communication except for the communication for emergency situation. Only the mobile station  200   a  which sent the communication for emergency situation establishes a channel to the base station  100.  After the establishment, the mobile station  200   a  which sent the communication for emergency situation performs communication according to the normal communication procedure.

TECHNICAL FIELD

The present invention relates to a communication control method and acommunication system of a base station and a mobile station in acommunication system. More specifically, it relates to a communicationcontrol method in CDMA communication system which is suitable forcommunication for emergency situation when compared with normalcommunication, and to a communication system including a base stationand mobile stations.

BACKGROUND ART

The near-far problem is always a problem in CDMA (Code Division MultipleAccess) system. If mobile stations transmit at the same power, the radiowave from mobile stations far from a base station is weak at the basestation and the radio wave from mobile stations near the base station isstrong at the base station, which causes the problem. This has not beena problem in the Frequency Division Multiple Access (hereafter describedas FDMA) and the Time Division Multiple Access (hereafter described asTDMA) being conventional multiplexing communication systems.

In FDMA, each mobile station uses a different frequency. Therefore, evenif strength of the radio wave from a far mobile station and strength ofthe radio wave from a close mobile station are different, the basestation can distinguish them according to frequencies.

In TDMA, each mobile station uses a different time slot. Therefore, theradio wave from a far mobile station and the radio wave from a closemobile station do not simultaneously come to the base station.Accordingly, even if strength of the radio wave from the distant mobilestation and strength of the radio wave from the close mobile station aredifferent, the base station can distinguish them according to timeslots.

On the other hand, in CDMA system, the base station simultaneouslycommunicates with a plurality of mobile stations using the samefrequency and different codes. Then, if the radio wave from a distantmobile station and the radio wave from a close mobile station comesimultaneously at the same frequency, the radio wave from the distantmobile station will be drowned out by the radio wave of the close mobilestation. This is an outline of the problem called the near-far problem.

To avoid the near-far problem, the following two methods are currentlyknown. One is the method of using an artificial satellite as a basestation and stations on the earth (the airspace also included) as mobilestations. In this case, as to all the mobile stations, the ratio of thedistance between the mobile station and the base station isapproximately constant. Therefore, even when CDMA system is used forcommunication, the near-far problem does not occur. This method is usedin GPS (Global Positioning System).

The other is the method in which mobile stations control their power byperforming communication between the mobile stations and the basestation and configuring feedback loops so that the field strength fromeach mobile station at the base station may become approximatelyconstant. This is called power control. As to the power control, thereare two type methods; open loop control and closed loop control. Thesemethods are used by a cellular system such as a cellular phone, and arepatents of Qualcomm Incorporated (in USA) (for example, refer to thePatent Document 1, the Patent Document 2, and the Patent Document 3).

-   Patent Document 1: International Publication WO 91/07037-   Patent Document 2: International Publication WO 92/21196-   Patent Document 3: International Publication WO 94/19876

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Conventionally, emergency communication etc. has been performed asfollows: The emergency communication etc. herein indicates one ofdistress communication, emergency communication, safety communication,and extraordinary communication defined by the Radio Law.

In FDMA, specific frequencies are defined to be emergency communicationfrequencies, and one is obliged to always monitor the emergencycommunication frequencies (Article 65 of the Radio Law). However,according to this method, it is prohibited to use the emergencycommunication frequency when emergency communication etc. is notperformed. That is, it is impossible to affirm that all the frequenciesare being utilized for communication.

Similarly, in TDMA, specific time slots are defined to be time slots foremergency and it is not allowed to use the time slots for emergencyexcept in an emergency. Thus, it is possible to perform emergencycommunication etc. However, according to this method, it is prohibitedto use the time slots for emergency when emergency communication etc. isnot performed. That is, it is impossible to affirm that all the time isutilized for communication.

Similarly, in the case of CDMA, specific codes are defined to be codesfor emergency and it is not allowed to use the codes for emergencyexcept in an emergency. Thus, it is possible to perform emergencycommunication etc. However, according to this method, it is prohibitedto use the code for emergency when emergency communication etc. is notperformed. That is, it is impossible to affirm that all the codes areutilized for communication.

As stated above, the problem common to the conventional methods is thatan emergency communication frequency in the case of FDMA, a time slotfor emergency in the case of TDMA, and a code for emergency in the caseof CDMA are reserved for emergency communication. In other words, a partof channel capacity that is assigned as a radio wave, which is limitedresource, is always reserved for emergency communication etc. seldomused. Such emergency communication is hereafter called the emergencycommunication of the channel capacity reservation type.

In the emergency communication of the channel capacity reservation type,partial channel capacity is reserved only for the time of performingemergency communication etc. rarely performed. Therefore, it isimpossible to utilize all the channel capacity for normal communication,which is inefficient in the respect of effective use of a radio wave,which is limited resource.

Furthermore, in the case of FDMA, it is necessary to always monitor theemergency communication frequency on which a call rarely exists, asdifferent one from normal communication. This gives a large burden to aperson who operates it.

The present invention aims at preferentially dealing with communicationfor emergency situation by a simple and effective method when emergencycommunication etc. is sent. A method of preferentially dealing withcommunication for emergency situation by a simple and effective method,especially in the case of using CDMA system for communication, isproposed.

Means to Solve the Problems

According to a mobile station of the present invention, the mobilestation which communicates with a base station includes:

an emergency communication call part to request to initiate a call ofcommunication for emergency situation, in time of emergency;

an output control part, in response to a request from the emergencycommunication call part, to control field strength of a signal to beused for the communication for emergency situation so that thecommunication for emergency situation will be established at the fieldstrength, with submerging communication between other mobile stationsand the base station; and

a mobile station side transmission part to transmit a call signal of thecommunication for emergency situation to the base station, at the fieldstrength controlled by the output control part.

Moreover, the output control part increases the field strength of thecall signal until the field strength becomes strong enough for a signalto be decoded, the signal being received by the base station from themobile station in case of the communication for emergency situation,with submerging a signal received by the base station from the mobilestation in case of normal communication.

Moreover, the output control part continues to retain the field strengthto be strong enough to establish the communication for emergencysituation with submerging the communication between the other mobilestations and the base station until the communication for emergencysituation with the base station is completed.

Moreover, the mobile station side transmission part transmitsidentification information indicating to be the communication foremergency situation, together with the call signal of the communicationfor emergency situation, at emergency field strength controlled by theoutput control part.

Moreover, after the mobile station side communication part transmits thecall signal of the communication for emergency situation, the outputcontrol part ignores a suppression signal of the field strengthtransmitted from the base station until channel for emergency situationto the base station is established in response to the call signal, andafter the channel for emergency situation is established, suppresses thefield strength to be normal field strength, and after the channel foremergency situation to the base station is established, the mobilestation side transmission part performs the communication for emergencysituation with the base station at the normal field strength controlledby the output control part.

Moreover, the mobile station side transmission part continues totransmit the call signal of the communication for emergency situation tothe base station at emergency field strength controlled by the outputcontrol part, until channel for emergency situation to the base stationis established.

Moreover, in time of an emergency of an aircraft or a ship, theemergency communication call part requests to initiate a call ofdistress communication as the call of the communication for emergencysituation, and the output control part, in response to the request ofthe emergency communication call part, controls the field strength usedfor communication with the base station so that the communication foremergency situation will be established at the field strength, withsubmerging the communication between the other mobile stations and thebase station.

Moreover, the emergency communication call part requests to initiate acall of at least one of emergency communication, safety communication,or extraordinary communication, as the call of the communication foremergency situation, and the output control part, in response to therequest of the emergency communication call part, controls the fieldstrength being an antenna power in a range not against laws and used forcommunication with the base station so that the communication foremergency situation will be established at the field strength, withsubmerging the communication between the other mobile stations and thebase station.

Moreover, according to the mobile station described in claim 1, theemergency communication call part requests to initiate a call of atleast one of emergency communication, safety communication, orextraordinary communication, as the call of the communication foremergency situation, and the output control part, in response to therequest of the emergency communication call part, controls the fieldstrength and used for communication with the base station by usingdirectivity of an antenna, so that the communication for emergencysituation will be established at the field strength, with submerging thecommunication between the other mobile stations and the base station.

According to a method for controlling mobile station side communicationof the present invention, the method for controlling mobile station sidecommunication which communicates with a base station includes:

requesting to initiate a call of communication for emergency situation,in time of emergency;

in response to the requesting to initiate the call of the communicationfor emergency situation, controlling field strength of a signal to beused for the communication for emergency situation so that thecommunication for emergency situation will be established at the fieldstrength, with submerging communication between other mobile stationsand the base station; and

transmitting a call signal of the communication for emergency situationto the base station, at the field strength controlled.

According to a base station of the present invention, the base stationwhich communicates with a plurality of mobile stations includes:

a base station side reception part to receive signals transmitted fromthe plurality of mobile stations;

a detection part to detect a call signal of communication for emergencysituation from the signals received by the base station side receptionpart, based on field strength of the signals received; and

a base station side transmission part to transmit an assignment signalfor assigning channel for emergency situation to a mobile station whichsent the call signal of the communication for emergency situationdetected by the detection part.

Moreover, the base station side transmission part transmits theassignment signal for assigning all or a part of assignable channel tothe mobile station which sent the call signal of the communication foremergency situation detected by the detection part.

Moreover, in case of the detection part detecting the call signal of thecommunication for emergency situation, the base station sidetransmission part transmits suppression signals of the field strength tothe plurality of mobile stations, and transmits the assignment signal tothe mobile station with which communication does not stop even by thesuppression signals of the field strength transmitted.

Moreover, the base station side transmission part transmits signalsdirecting a reduction of the field strength, a keeping of a presentcondition of the field strength, or a physical disconnection of normalcommunication, to mobile stations, as the suppression signals of thefield strength.

According to a method for controlling base station side communication ofthe present invention, the method for controlling base station sidecommunication which communicates with a plurality of mobile stationsincludes:

receiving signals transmitted from the plurality of mobile stations;

detecting a call signal of communication for emergency situation fromthe signals received, based on field strength of the signals received;and

transmitting an assignment signal for assigning channel for emergencysituation to a mobile station which sent the call signal of thecommunication for emergency situation detected.

According to a communication system of the present invention, thecommunication system where a base station and a plurality of mobilestations communicate comprises,

each mobile station of the plurality of mobile stations including:

an emergency communication call part to request to initiate a call ofcommunication for emergency situation, in time of emergency;

an output control part, in response to a request from the emergencycommunication call part, to control field strength to be used for thecommunication for emergency situation so that the communication foremergency situation will be established at the field strength, withsubmerging communication between other mobile stations and the basestation; and

a mobile station side transmission part to transmit a call signal of thecommunication for emergency situation to the base station, at the fieldstrength controlled by the output control part, and the base stationincluding:

a base station side reception part to receive signals transmitted fromthe plurality of mobile stations;

a detection part to detect a call signal of communication for emergencysituation from the signals received by the base station side receptionpart, based on field strength of the signals received; and

a base station side transmission part to transmit an assignment signalfor assigning channel for emergency situation to a mobile station whichsent the call signal of the communication for emergency situationdetected by the detection part.

Moreover, the communication system includes a plurality of basestations, and each base station of the plurality of base stations islocated so that a coverage area of the each base station may not overlapand independently performs normal communication and communication foremergency situation with the plurality of mobile stations existing inthe coverage area of the each base station.

According to a program for controlling mobile station side communicationof the present invention, the program, having computer executableprocessing, for controlling mobile station side communication, whichcommunicates with a base station, includes:

processing of requesting to initiate a call of communication foremergency situation, in time of emergency;

in response to the requesting to initiate the call of the communicationfor emergency situation, processing of controlling field strength of asignal to be used for the communication for emergency situation so thatthe communication for emergency situation will be established at thefield strength, with submerging communication between other mobilestations and the base station; and

processing of transmitting a call signal of the communication foremergency situation to the base station, at the field strengthcontrolled.

According to a program for controlling base station side communicationof the present invention, the program, having computer executableprocessing, for controlling base station side communication, whichcommunicates with a plurality of mobile stations, includes:

processing of receiving signals transmitted from the plurality of mobilestations;

processing of detecting a call signal of communication for emergencysituation from the signals received, based on field strength of thesignals received; and

processing of transmitting an assignment signal for assigning channelfor emergency situation to a mobile station which sent the call signalof the communication for emergency situation detected.

Effects of the Invention

According to the present invention, as it is unnecessary to alwaysreserve a part of channel capacity for emergency communication etc., thechannel resource that no longer needs to be reserved can be effectivelyused.

BEST MODE FOR CARRYING OUT THE INVENTION

In the communication system according to Embodiments explained below,the case of applying the present invention to an aviation field will bedescribed as an example. In this case, a ground station whichcommunicates with aircraft and a satellite station which communicateswith aircraft are called base stations, and an aircraft whichcommunicates with a base station is called a mobile station.

Moreover, it is assumed that a channel using CDMA system is establishedbetween mobile stations and a base station. The base station correspondsto a controller, the mobile stations correspond to pilots, and othersare equivalent to the conventional structure. Further, in thecommunication system according to Embodiment explained below, it isassumed that CDMA system is used and it is in a state of no near-farproblem, namely power control being performed or the base station beinga satellite.

In all the Embodiments explained below, communication for emergencysituation indicates distress communication, emergency communication,safety communication, and extraordinary communication. The distresscommunication indicates a method of preceding a distress signal at thetime when a ship or an aircraft is in grave and imminent danger. Theemergency communication indicates a method of preceding an emergencysignal at the time when a ship or an aircraft has a possibility oflapsing into grave and imminent danger or other emergency matter occurs.The safety communication indicates a method of preceding a safety signalfor the purpose of preventing grave danger against navigation of a shipor an aircraft. The extraordinary communication indicates radiocommunication performed for rescuing a human life, relieving at adisaster, reserving transportation and telecommunication, or retainingorder when it is impossible or remarkably difficult to utilize wiredcommunication, where an earthquake, a typhoon, a flood, a tidal wave,snow damage, a conflagration, a riot or any other emergencies occurredor anticipated to occur. Normal communication indicates communicationother than the communication for emergency situation.

Embodiment 1

Embodiment 1 will be explained hereafter. FIG. 1 illustrates normalcommunication of a base station 100 and a mobile station 200 structuringthe communication system according to Embodiment 1. The state isconsidered that the base station 100 communicates with n mobile stations(n is a natural number, which is 2 or greater than 2): a mobile station200 a, a mobile station 200 b, a mobile station 200 c, . . . , and amobile station 200 n. Normally, as shown in FIG. 1, all the mobilestations 200 perform normal communication with the base station 100.

Next, a method of the mobile station 200 a's performing communicationfor emergency situation will be described. FIG. 2 illustrates acommunication state when the mobile station 200 a sends communicationfor emergency situation. The mobile station 200 a temporarily increasesfield strength of a signal to be sent to the base station 100 from themobile station 200 a. This can be realized by a method, for example, inwhich the mobile station 200 a temporarily increases output, or changesa gain of an antenna by using an array antenna and such. At this time,it is supposed that the base station 100 continues to output a signalwhich controls all the mobile stations 200 to maintain the output levelhaving been kept.

According to a feature of CDMA system which is known as the near-farproblem, when field strength from only a certain mobile station becomesstrong, it becomes impossible for the base station to decode radio wavesfrom the other mobile stations. In the present case, when the radio wavefrom the mobile station 200 a at the base station 100 becomessufficiently strong compared with radio waves from the other mobilestations, it becomes impossible for the base station 100 to decode radiowaves of the mobile station 200 b, . . . , the mobile station 200 n.

Thus, the mobile station 200 a submerges communication between the basestation 100 and the other mobile stations 200 b, . . . , 200 n byincreasing the field strength of a call signal until a communicationsignal between the mobile station 200 a and the base station 100 becomesto have the field strength strong enough to be decoded, in order toestablish an exclusive channel which can use all the channel capacityfor the base station 100. When the mobile station is in the coveragearea of the base station, since a radio wave from the base stationreaches the mobile station, output control at the base station side isunnecessary.

Next, an internal structure of the base station 100 and the mobilestation 200 which compose the communication system of the presentEmbodiment will be explained with reference to FIG. 3.

The mobile station 200 utilizing CDMA needs an output control part 202which has a function of normal power control, i.e., controlling fieldstrength of a signal for performing normal communication, and a functionof temporarily increasing an output, with ignoring the normal powercontrol, by switching from the normal function to the emergency one. Inaddition, the mobile station 200 includes a communication control part204 which controls normal communication, an emergency communication callpart 206 which requests the output control part 202 to initiate a callof communication for emergency situation in time of emergency, a mobilestation side transmission part 208 which transmits a signal for radiocommunication with the base station 100, and a mobile station sidereception part 210 which receives a signal for radio communication withthe base station 100.

On the other hand, the base station 100 includes an output control part102 which controls field strength of a signal used for radiocommunication with the mobile station 200, a base station sidetransmission part 110 which transmits a signal for radio communicationwith the mobile station 200, a base station side reception part 108which receives a signal for radio communication with the mobile station200, a detection part 106 which detects a call signal of communicationfor emergency situation from the received signal based on the fieldstrength of the signal received by the base station side reception part108, and a communication control part 104 which controls normalcommunication.

Next, operations of the present communication system will be explained.The mobile station 200 a sends communication for emergency situation tothe base station 100 as follows:

-   (1) Corresponding to a call request of communication for emergency    situation sent from the emergency communication call part 206 in an    emergency, the output control part 202 switches the output    adjustment of field strength from the normal mode to the emergency    mode, submerges communication between the other mobile stations and    the base station 100, and increases the field strength used for the    communication for emergency situation until the field strength of    the communication signal in an emergency between the mobile station    concerned and the base station 100 becomes strong enough to be    decoded.-   (2) The mobile station side transmission part 208 sends a call    signal of the communication for emergency situation to the base    station 100, at the field strength controlled by the output control    part 202.-   (3) The base station side reception part 108 receives a strong radio    wave from the mobile station 200 a which sent the communication for    emergency situation.-   (4) The detection part 106 detects the call signal of the    communication for emergency situation in the received signal, based    on the field strength of the signal received by the base station    side reception part 108, and the base station side transmission part    110 continues to output suppression signals to all the mobile    stations for suppressing their field strength. At this time, the    base station side transmission part 110 sends signals to all the    mobile stations, as the suppression signals of the field strength,    which direct reduction of the field strength, keeping of the present    condition of the field strength (determent of the rise of the field    strength), or physical disconnection of the normal communication    with the other mobile stations.-   (5) The mobile station 200 a ignores this suppression signal for the    field strength, and since the other mobile stations are suppressed    by the near-far effect, it becomes impossible for the base station    100 to receive communication except for the communication for    emergency situation sent from the mobile station 200 a.-   (6) The base station side transmission part 110 transmits an    assignment signal for assigning channel for emergency situation to    the mobile station 200 a which sent the communication for emergency    situation detected by the detection part 106, and only the mobile    station 200 a which sent the communication for emergency situation    establishes a channel to the base station 100. The base station side    transmission part 110 can assign all or a part of assignable channel    to the mobile station 200 a. When the base station side transmission    part 110 assigns all of the assignable channel to the mobile station    200 a, the mobile station 200 a can quickly perform the    communication for emergency situation by using all of the channel.    When the base station side transmission part 110 assigns a part of    the channel to the mobile station 200 a, the communication for    emergency situation with the mobile station 200 a can be reserved    while retaining the normal communication of the other mobile    stations using the channel to the base station 100.-   (7) After establishing the channel for emergency situation to the    base station 100, the output control part 202 of the mobile station    200 a suppresses the field strength to be normal field strength, and    performs the communication for emergency situation with the base    station according to the normal communication procedure. However, it    is also acceptable for the output control part 202 to continue to    retain the field strength strong enough to establish the    communication for emergency situation, with submerging the    communication between the other mobile stations and the base station    100, until the communication for emergency situation with the base    station 100 is completed.

Next, in addition to the above communication procedure, the case ofrequesting a code allocation with initiating a call of communication foremergency situation will be explained with reference to FIG. 4. FIG. 4shows a communication procedure under the assumption of the case of themobile station 200 a sending communication for emergency situation. Thebold lines in FIG. 4 indicate that transmission is performed in anemergency by using a stronger output (field strength) than a normal one.

First, corresponding to a call request of communication for emergencysituation sent from the emergency communication call part 206 in anemergency, the output control part 202 switches the output adjustment offield strength from the normal mode to the emergency mode, submergescommunication between the other mobile stations and the base station100, and increases the field strength used for the communication foremergency situation until the field strength of the communication signalin an emergency between the mobile station concerned and the basestation 100 becomes strong enough to be decoded (S1).

The mobile station side transmission part 208 transmits a codeallocation request signal together with the call signal of thecommunication for emergency situation, at the field strength controlledby the output control part 202 (S2). The code allocation request signalis an example of identification information indicating to becommunication for emergency situation. Therefore, as long as the codeallocation request signal can inform the base station 100 that it is inan emergency, it may have any information.

The base station side reception part 108 receives a strong radio wavefrom the mobile station 200 a which sent the communication for emergencysituation (S3).

The detection part 106 detects the call signal of the communication foremergency situation in the received signal, based on the field strengthof the signal received by the base station side reception part 108, andthe base station side transmission part 110 continues to outputsuppression signals for suppressing field strength to the other mobilestations (S4).

As the other mobile stations are suppressed by the near-far effect, itbecomes impossible for the base station 100 to receive communicationexcept for the communication for emergency situation sent from themobile station 200 a (S5).

The base station side transmission part 110 transmits an assignmentsignal (code allocation) for assigning channel for emergency situationto the mobile station 200 a which sent the communication for emergencysituation detected by the detection part 106, and only the mobilestation 200 a which sent the communication for emergency situationestablishes a channel to the base station 100 (S6).

The mobile station side transmission part 208 transmits anacknowledgement signal (Ack) over the code allocation, to the basestation 100 (S7).

Then, it returns to the normal power-controlled state (field strength innormal time), which can minimize the interference to the communicationof the other mobile stations. Moreover, by this method, it is possibleto prepare for the case of other mobile station's sending communicationfor emergency situation. In this system, the communication is finallyperformed according to the normal communication procedure (S8). That is,the field strength of the mobile station 200 a, which sent thecommunication for emergency situation, finally becomes the same as theone power-controlled by the normal communication.

For this purpose, when a channel is established, a negotiation will beperformed between the mobile station 200 a and the base station 100, andthe mobile station 200 a will reserve only a necessary band (code) toperform communication for emergency situation. However, as mentionedabove, it is also acceptable for the mobile station 200 a to reserve allthe bands (codes) for the communication for emergency situation.

In the case of an aircraft or a ship sending distress communication, theantenna power does not necessarily need to be in the range described inthe radio station license. When a ship or an aircraft performs distresscommunication, the installation place of radio equipment, theidentification code, the type of a radio wave, a frequency, operationtime, and an antenna power do not need to comply with what is describedin the license. That is, it is possible to perform transmission at themaximum output technically possible which exceeds the output permittedby the license. Even if the transmission is performed at the technicallypossible maximum output, the Radio Law (Articles 52, 53, 54, 55, 56, 66,67, 68, 80, and 106) is not infringed.

Therefore, in the case of an emergency of an aircraft or a ship, whenthe emergency communication call part 206 requests a call of distresscommunication as a call of communication for emergency situation, theoutput control part 202 performs transmission, corresponding to therequest of the emergency communication call part 206, at a sufficientlylarge output (depending upon a receiver and a modulation system to beused, and a required error occurrence rate) of the field strength usedfor communication with the base station 100. Accordingly, it becomespossible to suppress radio waves from the other mobile stations (whichperform transmission at the antenna power described in the radio stationlicense). That is, the output control part 202 can perform transmissionwith setting the field strength output to the maximum of self-capacity.

However, this method intentionally blocks operations of other radiostations. Therefore, when the emergency communication call part 206requests a call of at least one of emergency communication, safetycommunication, or extraordinary communication, as a call ofcommunication for emergency situation, the output control part 202 needsto control the field strength used for communication with the basestation 100 as follows, corresponding to the request of the emergencycommunication call part 206. That is, the output control part 202 needsto control the field strength used for communication with the basestation 100 to be antenna power in the range not against laws, such asthe Radio Law, and field strength of establishing the communication foremergency situation with submerging communication between other mobilestations and the base station. In the case of performing communicationat excessive antenna power for uses other than distress communication inJapan, it is punished under Article 56 of the Radio Law.

The radio communication method and its communication system whichperforms distress communication, emergency communication, safetycommunication, extraordinary communication (communication for emergencysituation), normal communication and so on, by using a code divisionmultiple access (CDMA) system has been explained above. Features of theradio communication method and its communication system are as follows:being composed of the base station 100 and two or more mobile stations200 for performing radio communication, including a transceiver whichenables to communicate at field strength larger than that of the othermobile stations performing normal communication in the case of the basestation 100 and the mobile stations 200 performing communication otherthan the normal communication, and giving priority to the communicationwith the mobile station performing communication for emergency situationby submerging communication of the mobile station 200 which performsnormal communication with the base station 100 in radio waves ofemergency communication etc.

Moreover, has been explained the radio communication method and itssystem which includes the first step in which the mobile station 200measures the field strength from the base station 100 and calculatesproper transmission power corresponding to a distance from the basestation 100 at the normal communication, includes the means at a stronglevel exceeding the transmission power calculated in the first step, andincludes the means in the mobile station side to control communicationat transmission power larger than the transmission level at the normalcommunication.

According to the invention of the present Embodiment, firstly, it isunnecessary to always reserve a part of channel capacity for emergencycommunication etc., which is unlike the emergency communication of thechannel capacity reservation type. This greatly contributes to effectiveuse of frequency being a global subject.

Moreover, as to the channel exclusively established by this method, thewhole capacity of the channel can be exclusively used by one station.Explaining more precisely, since the mobile station that sends emergencycommunication etc. can freely select a code, the mobile station canarbitrarily set up a channel capacity. Such feature that the channelcapacity can be arbitrarily set up is peculiar to the CDMA system, andlarge-scale equipment is needed for realizing the same system in theTDMA system or the FDMA system.

Furthermore, the base station is released from the duty of listening toemergency communication frequency, which is an indispensable duty inFDMA.

Embodiment 2

In the present Embodiment, the situation that communication foremergency situation may be called from two or more mobile stations 200will be considered. FIG. 5 shows a whole structure of a communicationsystem where a plurality of mobile stations initiate calls ofcommunication for emergency situation.

For the communication for emergency situation sent from the first mobilestation 200 a, a channel is established like the above stated. For thecommunication for emergency situation sent from the second mobilestation 200 n, the following procedures are added according to thepresent Embodiment.

In the case the mobile station 200 n fails in reserving an exclusivechannel to the base station 100 a, it tries to reserve an exclusivechannel to the base station 100 a at a certain time interval (timeinterval is determined at random) as an example stated above until itreserves it.

At the time of the first mobile station 200 a reserving a channel andperforming a negotiation (establishment of channel for emergencysituation), the first mobile station 200 a reduces the output (fieldstrength).

The mobile station side transmission part 208 of the second mobilestation 200 n continues to transmit a call signal of communication foremergency situation to the base station 100 at the field strengthcontrolled by the output control part 202 until channel for emergencysituation to the base station 100 a is established. Therefore, after thefirst mobile station 200 a reduces the field strength, the mobilestation side transmission part 208 of the second mobile station 200 ncan reserve the channel to the base station 100 a. At this time, itshould be noticed that distribution of the channel capacity (in the caseof CDMA, determination of a code) may be concerned by the base station.

In addition, it is also possible for the base station 100 a to acceptthe emergency call signal from the second mobile station 200 n, sentduring the communication for emergency situation between the firstmobile station 200 a and the base station 100 a, while the first mobilestation 200 a and the base station 100 perform communication foremergency situation. In this case, since the time period in which thecommunication for emergency situation with the first mobile station 200a is broken by the emergency call signal from the second mobile station200 n is at most about 100 milliseconds, it does not cause a largetrouble to the communication between the first mobile station 200 a andthe base station.

Thus, it becomes possible for the base station 100 a to performcommunication for emergency situation with the first mobile station 200a and communication for emergency situation with the second mobilestation 200 n in parallel, by accepting the emergency call signal of thesecond mobile station 200 n during the communication with the firstmobile station 200 a.

Moreover, in the cellular system, if coverage areas of base stations aredivided not to overlap, the problem in the case of many base stationsexisting can be reduced to the case of only one base station. In thiscase, the shape of a cell can be other than Voronoi Division being theoptimal shape.

Voronoi Division is a division composed of line segments ofperpendicular bisectors for adjacent P_(i) and P_(j)'s, for {P_(i)}being a set of P_(i), where i is a natural number and P_(i) is a pointindicating the base station 100 in this case. The polygon made by thisdivision is called a Voronoi polygon and the diagram showing the wholedivision is called a Voronoi diagram. FIG. 6 shows an example of theVoronoi diagram where P₀, . . . , P₅ are generatrices.

In the cellular system, as mentioned above, the method for communicationfor emergency situation described in each Embodiment for the mobilestation 200 a and the mobile station 200 b which communicate with thebase station P₀ can be established in connection with a base station P₄even when the mobile station 200 a and the mobile station 200 b move tothe base station P₄ as shown in FIG. 6. That is, the communication foremergency situation between the base station P₀ and a mobile station inthe cell of the base station P₀ and the communication for emergencysituation between the base station P₄ and a mobile station in the cellof the base station P₄ are independent of each other.

Therefore, the method in which the base station 100 a establisheschannel for emergency situation shown in FIG. 5 can also be establishedby the base station 100 b in the same way. The base station 100 a andthe base station 100 b are controlled by a central control system 400.

As stated above, have been explained in the present Embodiment the radiocommunication method and its system which include means to transmit arequest code (code allocation request) from the mobile station 200 in anemergency, not the time of normal communication, with initiating a callof communication for emergency situation, to transmit a power controlbit (suppression signal of field strength) from the base station 100 byinserting the power control bit into the communication channel, and tocontrol transmission power of other mobile stations.

Moreover, have been explained the radio communication method and itssystem which include means to control transmission power of normalcommunication and emergency communication etc., with the mobile station200's checking establishment or failure of an emergency channel etc.,and enable a plurality of mobile stations in the same base station toperform emergency communication by initiating a call of emergencycommunication etc. at a certain fixed interval until the emergencychannel etc. is established.

According to the present Embodiment, since a flag (request code)indicating to be an emergency is transmitted to the base station 100with a call of communication for emergency situation, the base station100 can clearly recognize a request of communication for emergencysituation.

Moreover, according to the present Embodiment, in the case of the radionetwork made by the cellular system, since the influence of emergencycommunication etc. is not exerted on the cell which is far from thestation performing emergency communication etc., it is possible togreatly contribute to effective use of frequency.

Embodiment 3

In the above Embodiments, the method in which the mobile station 200 aperforms communication for emergency situation with the base station 100by displacing the communication with other mobile stations bytemporarily increasing the output has been described. In the presentEmbodiment, this method is applied to the calling of normalcommunication. The core of the idea is to make the output of the mobilestation performing normal communication lower than the conventional one,not to make the output of the mobile station 200 performing thecommunication for emergency situation larger than the conventional one.

The case that two or more mobile stations 200 exist in the coverage areaof one base station 100 will be considered. As mentioned above, it canbe thought that even if the number of the base stations increases, it isreduced to the case of one base station because the space can be dividedinto coverage areas (cellular system). That is, one base station systemcan be assumed without loss of generality.

The size of a coverage area covered by one base station 100 is set to besmaller than that of the normal system. Then, in performingcommunication between the base station 100 and the mobile station 200,it is enough to transmit at power (field strength) smaller than that ofthe normal system. Concretely, normal communication is performed withrecognizing 1/n (n is a ratio of power required for performingsuppression using the near-far problem) of the maximum power of themobile station side used in the normal system, as the maximum powerallowed for the mobile station.

When the mobile station 200 establishes communication with the basestation 100, transmission is performed at the maximum power equivalentto that of the normal system. At this time, it is assumed that the basestation 100 continues to output suppression signals to all the mobilestations 200 for suppressing their outputs.

By doing this, an exclusive channel to the base station 100 can beestablished, with temporarily suppressing communication of the othermobile stations like a previous example. Such establishment of anexclusive channel is utilized for initiating a call to the base stationfrom the mobile station 200.

When performing this call, though the channel temporarily becomessuspended, after the mobile station having performed the call returns toa normal output (normal field strength), the other mobile stations canreturn to the normal communication. If this communication is datacommunication of a packet system, even when the communicationtemporarily becomes suspended, the communication can be performed likethat of before the call, after the channel has recovered. Then, thetemporal suspension of the communication does not become a largeproblem.

Moreover, although a short-time (normally about 100 milliseconds)disconnection occurs in the communication with a circuit switchingsystem, such as a telephone, if the disconnection time is small, onewould not be greatly annoyed while on the telephone and can practicallyuse it without any problem.

According to the present Embodiment, a call can be performed by theabove-mentioned procedure without using a control channel. The controlchannel is a special channel which is not used for communication. Sincecommunication can be performed without using the control channel (apower control signal can be superimposed on normal communication), it ispossible to use all the assigned frequencies for the communication.Therefore, the band (channel capacity) having been used as a controlchannel can be used for normal communication. Consequently, it cangreatly contribute to the effective use of the frequency.

Moreover, according to the present Embodiment, because the fieldstrength of the mobile station performing normal communication is madeto be lower than the conventional one, not because the field strength ofthe mobile station 200 performing communication for emergency situationis made to be larger than the conventional one, the amount of powerrequired for the whole communication system can be reduced.

Embodiment 4

In the present Embodiment, will be explained the communication method inwhich a mobile station to send a signal of communication for emergencysituation firstly sends a noise in order to interfere with the normalcommunication between other mobile stations and the base station, andthen stops a noise to send information on the communication foremergency situation.

The case that two or more mobile stations 200 exist in the coverage areaof one base station 100 will be considered. As mentioned above, it canbe thought that even if the number of the base stations 100 increases,it is reduced to the case of one base station because the space can bedivided into coverage areas (cellular system). That is, also in thepresent Embodiment, one base station system can be assumed without lossof generality.

It is assumed that the base station 100 communicates with n mobilestations (n is a natural number, which is 2 or greater than 2): a mobilestation 200 a, a mobile station 200 b, . . . , and a mobile station 200c. Normally, as shown in FIG. 1, all the mobile stations 200 performnormal communication with the base station. A method of the mobilestation 200 a's performing communication for emergency situation in thiscase will be explained with reference to FIG. 7.

FIG. 7 shows a sending procedure of the communication for emergencysituation by interfering according to the present Embodiment. First, atthe mobile station 200 a side, corresponding to a call request of thecommunication for emergency situation sent from the emergencycommunication call part 206, the following is performed in an emergency:the output control part 202 switches the output adjustment of fieldstrength from the normal mode to the emergency mode, and controls thefield strength used for the communication for emergency situation to bestrong enough to interfere with communication between the other mobilestations and the base station 100 (S1), and the mobile station sidetransmission part 208, by outputting a signal at strong field strength,interferes with communication from the other mobile stations (in FIG. 1,the mobile station 200 b, . . . , the mobile station 200 n) to the basestation 100 (S12). It is based on the characteristic of the CDMA systemthat it is easy to interfere with communication with other mobilestations. This interference does not need to include the contents ofcommunication (a flag indicating to be communication for emergencysituation) which is included in Embodiment 2, and it is acceptable forthe interference to be a noise indicating arbitrary contents orindicating nothing. The noise needs to be transmitted at the fieldstrength strong enough to interfere with communication between the basestation 100 and the other mobile stations.

In the case of transmitting a sign indicating communication foremergency situation or terminal information of the mobile station 200 a,as a flag indicating to be communication for emergency situation, whichshould be included in the communication system according to Embodiment2, not in the similar type of the present Embodiment.

In response to the above noise, the base station 100 transmitssuppression signals of field strength to all the mobile stations forinstructing to reduce outputs (field strength) (S13).

According to the output reduction instruction, mobile stations otherthan the mobile station 200 a reduce field strength in response to thesuppression signals, so that signals from the other mobile stations stopreaching the base station 100 and the communication stops (S14).

In the meantime, the mobile station 200 a ignores the suppressionsignals of field strength from the base station 100, and transmits notan interference wave (noise), but the contents of the communication foremergency situation to the base station 100 at the maximum outputpermitted in an emergency (S15). It is assumed that the base stationcontinues to output the output reduction instructions.

By detecting that links with the other mobile stations are disconnected,the base station 100 recognizes that the request of communication foremergency situation is sent from the mobile station 200 a (S14, S15).

Moreover, according to the power control patents of Qualcomm, since thetime constant of output rise is longer than the time constant of outputreduction, the mobile station 200 a can obtain an output relativelylarger than the other mobile stations until the other mobile stationsreturn outputs to the original ones. Therefore, even if the base station100 does not send output reduction instructions, the base station 100can recognize that the request of communication for emergency situationis sent from the mobile station 200 a.

After this, the channel is established like Embodiment 1, and thecommunication for emergency situation is performed based on the normalcommunication procedure.

According to the present Embodiment, the mobile station 200 a requestingthe communication for emergency situation can inform the base station100 that the mobile station 200 a is requesting to establish channel foremergency situation, by outputting only the noise to interfere withnormal communication between other mobile stations and the base station100, without including the contents notifying the emergency in thesignal.

The communication systems according to all the Embodiments stated abovecan also be realized by the internal structure of the base station 100and the mobile station 200 as shown in FIG. 8.

In the communication system shown in FIG. 8, compared with the mobilestation 200 of FIG. 3, the output control part 202 and the emergencycommunication call part 206 do not exist in the mobile station 200, andinstead of them, an emergency communication management part 300 isneeded between the mobile station 200 and the base station 100.

The emergency communication management part 300 includes an emergencycommunication call part 302 and an amplifier 304. In time of emergency,the emergency communication call part 302 requests to initiate a call ofcommunication for emergency situation, and has the same function as theemergency communication call part 206 in the internal structure of themobile station 200 of FIG. 3. In response to the call request of thecommunication for emergency situation sent from the emergencycommunication call part 302, the amplifier 304 amplifies the power ofthe signal (the call signal of communication for emergency situation)transmitted from the mobile station side transmission part 208 to befield strength strong enough to interfere with communication betweenother mobile stations and the base station 100.

The base station side reception part 108 receives the call signal ofcommunication for emergency situation amplified by the emergencycommunication management part 300. Subsequent operations are the same asthose in Embodiment mentioned above. Compared with the base station 100shown in FIG. 3, the output control part 102 is unnecessary for the basestation 100 shown in FIG. 8.

The internal structure of the mobile station 200 can be simplified bystructuring the communication system as shown in FIG. 8. Since users'requirements of reduction in weight and downsizing of volume for themobile station 200 are high, such users' requirements can be satisfiedwith the communication system illustrated in FIG. 8.

In all the Embodiments described above, explanations are provided withreference to CDMA as an example. Since a plurality of mobile stationsuse the same frequency simultaneously in CDMA, it is possible tosubmerge all communication of other mobile stations by the near-farproblem, and since the near-far problem occurs easily in CDMA, CDMA is acommunication method especially suitable for the invention described inthe Embodiments. However, the present invention is not limited to CDMA,and is applicable to any communication method as long as the near-farproblem occurs in the communication method. While there are severalmethods in CDMA, it is preferable for the present invention to use thedirect spread system used by many systems.

Moreover, according to the communication system of all the Embodiments,even if a method in which, in order to cope with the near-far problem,communication is performed between mobile stations and a base station,feedback loops are configured so that the field strength of each mobilestation at the base station may become approximately constant, andoutputs are adjusted at the mobile station sides (power control system)is adopted, the present invention can be utilized. Also, even if asystem using the power control system or a method of using an artificialsatellite as a base station and stations on the earth (the airspace alsobeing included) as mobile stations is adopted, the present invention canbe utilized.

Moreover, in all the Embodiments, the field strength which is output bythe mobile station 200 and is strong enough to interfere withcommunication between the other mobile stations and the base station 100in an emergency may be about one hundred times the field strength usedfor normal communication. Specifically, it may be about 20 dB. In thecase of distress communication, the field strength used for thecommunication for emergency situation is assumed to be about 10 KW,whereas the field strength used for normal communication by the mobilestation 200 is about 100W.

In the communication systems according to all the Embodiments mentionedabove, the following can be considered as an example of the method ofthe mobile station 200's initiating a call of communication foremergency situation: an emergency button is provided in the interface ofthe mobile station 200, a function to transmit a signal storing dataindicating an emergency is linked to the emergency button, and thecommunication for emergency situation is called by a user's pushing theemergency button.

The communication systems according to all the Embodiments can berealized with a small revision of the communication systemconventionally used. Therefore, when applying the communication systemaccording to the present invention to communication using CDMA system,it is possible to preferentially deal with communication for emergencysituation using a comparatively simple protocol. Although thecommunication control method according to the present invention issimple, the following can be realized: easy implementation because ofthe simplicity, cost reduction, and high reliability in terms of thenumber of parts being small.

FIG. 9 shows a computer basic structure of the base station 100 and themobile station 200. In FIG. 9, a CPU 40 which executes programs isconnected with a monitor 41, a keyboard 42, a mouse 43, a communicationport 44, a magnetic disk drive 46, etc. through a bus 38. An OS 47, aprogram group 49, and a file group 50 are stored in the magnetic diskdrive 46. The form in which the program group 49 and the file group 50are united to be an object-oriented program group 49 can be consideredas one of the Embodiments.

In the case that each part structuring the base station 100 and themobile station 200 is implemented with a program, the present inventionis executed, for instance, by storing a program in which operations tobe executed by the output control part 202 are coded and a program inwhich operations to be executed by the emergency communication call part206 and so on are coded in the magnetic disk drive 46 as the programgroup 49, and by executing each program stored in the magnetic diskdrive 46 with the CPU 40 and the OS47.

In each of the above-mentioned Embodiments, the base station 100 and themobile station 200 use the function of the communication port 44, andradio communication is performed.

In all the Embodiments, each operation of each structure element relatesto each other, and taking the relation of the operations stated aboveinto consideration, the operation of each structure element can bereplaced as a series of operations. And such replacement enables them tobe Embodiments of a method invention.

Moreover, replacement of the operation of each structure element byprocessing of each structure element enables them to be Embodiments of aprogram.

Moreover, by storing the program in a computer-readable recording mediumin which a program is stored, they can be Embodiments of acomputer-readable recording medium stored in a program.

Therefore, the Embodiment of the program for controlling mobile stationside communication can be an Embodiment of a computer-readable recordingmedium storing a program for controlling mobile station sidecommunication, wherein the computer-readable recording medium stores theprogram, to be executed by a computer, for controlling mobile stationside communication, which communicates with a base station, including:

processing of requesting to initiate a call of communication foremergency situation, in time of emergency;

in response to the requesting to initiate the call of the communicationfor emergency situation, processing of controlling field strength of asignal to be used for the communication for emergency situation so thatthe communication for emergency situation will be established at thefield strength, with submerging communication between other mobilestations and the base station; and

processing of transmitting a call signal of the communication foremergency situation to the base station, at the field strengthcontrolled by the output control part.

Therefore, the Embodiment of the program for controlling base stationside communication can be an Embodiment of a computer-readable recordingmedium storing a program for controlling base station sidecommunication, wherein the computer-readable recording medium stores theprogram, to be executed by a computer, for controlling base station sidecommunication, which communicates with a plurality of mobile stations,including:

processing of receiving signals transmitted from the plurality of mobilestations;

processing of detecting a call signal of communication for emergencysituation from the signals received, based on field strength of thesignals received; and

processing of transmitting an assignment signal for assigning channelfor emergency situation to a mobile station which sent the call signalof the communication for emergency situation detected.

Embodiment of a program and Embodiment of a computer-readable recordingmedium stored in a program can be structured by a program the entiretyof which is operable in a computer. Each processing in Embodiment of aprogram and Embodiment of computer-readable recording medium storing aprogram can be executed by a program, which is stored in a recordingdevice, loaded from the recording device into a central processing unit(CPU), and executed by the central processing unit.

Moreover, it is also acceptable to realize software and a program ofeach Embodiment by firmware stored in ROM (READ ONLY MEMORY). Otherwise,it is also acceptable to realize each function of the program mentionedabove by a combination of software, firmware, and hardware.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows normal communication of a base station and a mobilestation;

FIG. 2 shows a communication state when a mobile station sendscommunication for emergency situation;

FIG. 3 shows an internal structure of a base station and a mobilestation;

FIG. 4 shows a procedure under the assumption of the case of a mobilestation sending distress communication;

FIG. 5 shows a whole structure of communication system where a pluralityof mobile stations send communication for emergency situation;

FIG. 6 is Voronoi Diagram where P₀-P₅ are generatrices;

FIG. 7 shows sending procedure of communication for emergency situationby interfering;

FIG. 8 shows another internal structure of a base station and a mobilestation; and

FIG. 9 shows a computer basic structure of a base station and a mobilestation.

1. A mobile station which communicates with a base station comprising:an emergency communication call part to request to initiate a call ofcommunication for emergency situation, in time of emergency; an outputcontrol part, in response to a request from the emergency communicationcall part, to control field strength of a signal to be used for thecommunication for emergency situation so that the communication foremergency situation will be established at the field strength, withsubmerging communication between other mobile stations and the basestation; and a mobile station side transmission part to transmit a callsignal of the communication for emergency situation to the base station,at the field strength controlled by the output control part, whereinafter the mobile station side communication part transmits the callsignal of the communication for emergency situation, the output controlpart ignores a suppression signal of the field strength transmitted fromthe base station until channel for emergency situation to the basestation is established in response to the call signal, and after thechannel for emergency situation is established, suppresses the fieldstrength to be normal field strength, and after the channel foremergency situation to the base station is established, the mobilestation side transmission part performs the communication for emergencysituation with the base station at the normal field strength controlledby the output control part.
 2. The mobile station of claim 1, whereinthe output control part increases the field strength of the call signaluntil the field strength becomes strong enough for a signal to bedecoded, the signal being received by the base station from the mobilestation in case of the communication for emergency situation, withsubmerging a signal received by the base station from the mobile stationin case of normal communication.
 3. The mobile station of claim 1,wherein the output control part continues to retain the field strengthto be strong enough to establish the communication for emergencysituation with submerging the communication between the other mobilestations and the base station until the communication for emergencysituation with the base station is completed.
 4. The mobile station ofclaim 1, wherein the mobile station side transmission part transmitsidentification information indicating to be the communication foremergency situation, together with the call signal of the communicationfor emergency situation, at emergency field strength controlled by theoutput control part.
 5. The mobile station of claim 1, wherein themobile station side transmission part continues to transmit the callsignal of the communication for emergency situation to the base stationat emergency field strength controlled by the output control part, untilchannel for emergency situation to the base station is established. 6.The mobile station of claim 1, wherein in time of an emergency of anaircraft or a ship, the emergency communication call part requests toinitiate a call of distress communication as the call of thecommunication for emergency situation, and the output control part, inresponse to the request of the emergency communication call part,controls the field strength used for communication with the base stationso that the communication for emergency situation will be established atthe field strength, with submerging the communication between the othermobile stations and the base station.
 7. The mobile station of claim 1,wherein the emergency communication call part requests to initiate acall of at least one of emergency communication, safety communication,or extraordinary communication, as the call of the communication foremergency situation, and the output control part, in response to therequest of the emergency communication call part, controls the fieldstrength being an antenna power in a range not against laws and used forcommunication with the base station so that the communication foremergency situation will be established at the field strength, withsubmerging the communication between the other mobile stations and thebase station.
 8. The mobile station of claim 1, wherein the emergencycommunication call part requests to initiate a call of at least one ofemergency communication, safety communication, or extraordinarycommunication, as the call of the communication for emergency situation,and the output control part, in response to the request of the emergencycommunication call part, controls the field strength being an antennapower in a range not against laws and used for communication with thebase station by using directivity of an antenna, so that thecommunication for emergency situation will be established at the fieldstrength, with submerging the communication between the other mobilestations and the base station.
 9. A method for controlling mobilestation side communication, which communicates with a base station,comprising: requesting to initiate a call of communication for emergencysituation, in time of emergency; in response to the requesting toinitiate the call of the communication for emergency situation,controlling field strength of a signal to be used for the communicationfor emergency situation so that the communication for emergencysituation will be established at the field strength, with submergingcommunication between other mobile stations and the base station;transmitting a call signal of the communication for emergency situationto the base station, at the field strength controlled; and ignoring asuppression signal of the field strength transmitted from a base stationuntil a channel for emergency situation to the base station isestablished in response to the call signal, and after the channel foremergency situation is established, suppressing the field strength to benormal field strength, and wherein after the channel for emergencysituation to the base station is established, a mobile station sidetransmission part performs the communication for emergency situationwith the base station at the normal field strength controlled by anoutput control part.
 10. A base station which communicates with aplurality of mobile stations comprising: a base station side receptionpart to receive signals transmitted from the plurality of mobilestations; a detection part to detect a call signal of communication foremergency situation from the signals received by the base station sidereception part, based on field strength of the signals received; and abase station side transmission part to transmit an assignment signal forassigning channel for emergency situation to a mobile station which sentthe call signal of the communication for emergency situation detected bythe detection part, wherein, in case of the detection part detecting thecall signal of the communication for emergency situation, the basestation side transmission part transmits suppression signals of thefield strength to the plurality of mobile stations, and transmits theassignment signal to the mobile station with which communication doesnot stop even by the suppression signals of the field strengthtransmitted.
 11. The base station of claim 10, wherein the base stationside transmission part transmits the assignment signal for assigning allor a part of assignable channel to the mobile station which sent thecall signal of the communication for emergency situation detected by thedetection part.
 12. The base station of claim 10, wherein the basestation side transmission part transmits signals directing a reductionof the field strength, a keeping of a present condition of the fieldstrength, or a physical disconnection of normal communication, to mobilestations, as the suppression signals of the field strength.
 13. A methodfor controlling base station side communication, which communicates witha plurality of mobile stations, comprising: receiving signalstransmitted from the plurality of mobile stations; detecting a callsignal of communication for emergency situation from the signalsreceived, based on field strength of the signals received; upondetection of communication for emergency, transmitting suppressionsignals of the field strength to the plurality of mobile stations; andtransmitting an assignment signal for assigning channel for emergencysituation to a mobile station which sent the call signal of thecommunication for emergency situation detected.
 14. A communicationsystem where a base station and a plurality of mobile stationscommunicate comprising, each mobile station of the plurality of mobilestations including: an emergency communication call part to request toinitiate a call of communication for emergency situation, in time ofemergency; an output control part, in response to a request from theemergency communication call part, to control field strength to be usedfor the communication for emergency situation so that the communicationfor emergency situation will be established at the field strength, withsubmerging communication between other mobile stations and the basestation and to ignore a suppression signal of the field strengthtransmitted from the base station until a channel for emergencysituation to the base station is established in response to the callsignal; and a mobile station side transmission part to transmit a callsignal of the communication for emergency situation to the base station,at the field strength controlled by the output control part, and thebase station including: a base station side reception part to receivesignals transmitted from the plurality of mobile stations; a detectionpart to detect a call signal of communication for emergency situationfrom the signals received by the base station side reception part, basedon field strength of the signals received and to transmit suppressionsignals to the plurality of mobile stations upon detection of a callsignal of communication for emergency situation; and a base station sidetransmission part to transmit an assignment signal for assigning channelfor emergency situation to a mobile station which sent the call signalof the communication for emergency situation detected by the detectionpart.
 15. The communication system of claim 14, wherein thecommunication system includes a plurality of base stations, and eachbase station of the plurality of base stations is located so that acoverage area of the each base station may not overlap and independentlyperforms normal communication and communication for emergency situationwith the plurality of mobile stations existing in the coverage area ofthe each base station.
 16. A computer readable medium having storedthere on a program, having computer executable instructions, forcontrolling mobile station side communication, which communicates with abase station, comprising: processing of requesting to initiate a call ofcommunication for emergency situation, in time of emergency; in responseto the requesting to initiate the call of the communication foremergency situation, processing of controlling field strength of asignal to be used for the communication for emergency situation so thatthe communication for emergency situation will be established at thefield strength, with submerging communication between other mobilestations and the base station and processing of ignoring a suppressionsignal of the field strength transmitted from the base station until achannel for emergency situation to the base station is established inresponse to the call signal; and processing of transmitting a callsignal of the communication for emergency situation to the base station,at the field strength controlled.
 17. A computer readable medium havingstored thereon a program, having computer executable instructions, forcontrolling base station side communication, which communicates with aplurality of mobile stations, comprising: processing of receivingsignals transmitted from the plurality of mobile stations; processing ofdetecting a call signal of communication for emergency situation fromthe signals received, based on field strength of the signals receivedand processing of transmitting suppression signals to the plurality ofmobile stations upon detection of a call signal of communication foremergency situation; and processing of transmitting an assignment signalfor assigning channel for emergency situation to a mobile station whichsent the call signal of the communication for emergency situationdetected.